This is a continuing project in research on the pathology of congenital heart disease on a city-wide basis. It is aimed at those anatomic data which are useful to clinicians and surgeons. Research is also carried on on the conduction system in congenital and acquired heart disease, from the standpoint of electrocardiographic and his bundle correlation. This research deals especially with congenital and acquired AV block and Wolff-Parkinson-White syndrome.